Wireless mobile terminals are widely used for voice, data and/or multimedia communications. As used herein, wireless mobile terminals may include conventional cell phones, Personal Communications Systems (PCS)/smart phones that may include data processing, voice, video, text message, e-mail and/or Web access capabilities, Personal digital Assistants (PDA) with wireless communications capabilities, wireless pagers, Blackberry wireless handheld e-mail devices, and/or laptop computers and/or other devices that may include a radiotelephone transceiver.
Wireless mobile terminals may be required to meet various standards promulgated by industry groups. One such standard is known as “conducted performance”. The conducted performance standard may define performance requirements that a wireless mobile terminal must pass when terminated in a reference impedance of 50 ohms. As a power amplifier in a wireless mobile terminal is designed to operate into a given load impedance, a fixed RF matching network may be provided to optimize the power amplifier performance when the antenna port is terminated with 50 ohms.
However, when an actual antenna is installed, the power amplifier of the wireless mobile terminal may not be terminated with a 50 ohm impedance. An impedance mismatch between the antenna and the power amplifier may result in non-optimal power transfer to the antenna. More particularly, this may result in degraded amplifier output power (Pout) and Power Added Efficiency (PAE), which, in turn, may result in lower Total Radiated Power (Trp) output. In other words, “over-the-air” (OTA) performance may be reduced, which may not satisfy user expectations.
An additional complication which may arise in wireless mobile terminals is that the antenna environment may be constantly changing, due to the changing proximity of the antenna to the head, hands, fingers, and/or other obstacles. This time-domain antenna environment variability translates into a time-domain antenna port impedance variance. As discussed above, such an impedance mismatch may cause power reflections at the point of connection that may result, for example, in reduced efficiency, bandwidth, and/or reduced signal-to-noise ratio.
As such, simultaneous optimization for both the conducted and OTA performance requirements may be difficult. Accordingly, as a compromise, fixed impedance matching networks have been used to trade-off some conducted performance for improved OTA performance. In addition, variable impedance matching networks have been utilized in wireless mobile terminals to match the impedance of the load in changing antenna environmental conditions.
However, due to the size constraints of modern wireless mobile terminals, it may be impractical to implement fixed and/or variable matching networks therein. Moreover, parasitic effects (due to undesired capacitance, inductance, and/or resistance) which may result from implementation of such matching networks may degrade antenna radiated efficiency and thereby compromise OTA performance, which may lead to user dissatisfaction.